Fires can occur at any location combustible materials are present and, unless extinguished, will usually increase and spread until all available combustible material present or within a drift range of burning or heated particles is ignited and then consumed. The conventional method of combating fires is to spray large volumes of water (sometimes including small amounts of other chemicals) on the combustible material at the base of the fire (e.g. for rapid cooling) and on combustible material above and adjacent the fire (e.g. to reduce likelihood of combustion and spreading of the fire. In most areas where population density is at least moderate or higher, water is generally supplied through a network of pipes or distribution systems for potable water and made available at fittings known as hydrants located periodically along such pipes or distribution systems; allowing trained personnel to attach hoses to convey water from the hydrants to the proximity of a fire.
As a matter of convenience, visibility and accessability of hydrants, such pipes or distribution systems are usually installed along one side of a street, road or other thoroughfare. However, since fires can occur at any location where combustible materials are present, such a location for hydrants requires that one or more hoses be positioned across such thoroughfares in order to carry water to the location of the fire in a substantial fraction of fire occurrences. While hoses generally used in fire-fighting are of very robust construction, allowing traffic to pass over them is highly undesirable due to the potential for damage to the hoses, which are quite expensive. Further, compression of a hose by the weight of a vehicle reduces or halts water flow in the hose and, in any case, causes substantial fluctuations in pressure which can impair operation of or cause damage to pumping equipment or other water conveying devices.
Therefore, in instances where one or more hoses must cross a thoroughfare, traffic must be halted or re-routed until some protective cover for the hose, referred to as a hose bridge, can be installed. Such devices typically form a ramp on opposite sides of a hose and a structural connection between the ramps and above the hose that will bear the weight of a vehicle and are thus structural “bridges” over hoses which are generally in use and filled with water at an elevated pressure when the hose bridges are installed.
While several designs of hose bridges are known and commercially available, such hose bridges present some difficulties and shortcomings in deployment and use. One major difficulty at the present time is the need to protect hoses of a nominally five inch diameter which are in widespread use at the present time to reduce pressure loss (e.g. in comparison with smaller standard diameter hoses) at high-volume flow rates. For example, one known form of hose bridge is formed in pairs to be located where vehicle tires are likely to pass with each hose bridge of the pair comprising a plurality of interlocking aluminum extrusions of limited length (e.g. about eighteen inches) to minimize storage space. This type of hose bridge is generally of a weight that can be handled by a single person but spacing of the hose bridges of a pair is somewhat critical to match the separation of tires on a vehicle axle so that the vehicle tires do not, in fact, contact the hose. Further, no protection is provided for the hose between the hose bridges. That is, when one axle of a vehicle has passed over the hose bridge but another axle of the vehicle has not yet reached the hose bridge, clearance of the vehicle above the hose is minimized (especially if the vehicle suspension allows some degree of recoil) and structure of the bottom of the vehicle body between the wheels may contact and damage the hose.
An alternative commercially available hose ramp comprises somewhat longer (e.g. about seventy inches) ramp-shaped sections of steel or aluminum having grooves or passages on the underside to accommodate hoses of different diameters and which can be interlocked to provide a hose bridge which is wider than roadway vehicles. Vertical apertures are formed therein to reduce weight and improve traction but sections of this type of hose bridge nevertheless weigh about sixty pounds each or a total of two hundred forty pounds for the complete hose bridge, compromising assembly, as does the need to align hoses with the grooves or passages.
It should be appreciated that either of these commercially available types of hose bridge requires material above the hose as well as spacing from the hose to allow for some deformation under load of the hose bridge without compressing the hose. Therefore, the overall height of either of these types of hose bridge, to accommodate a nominal five inch outside diameter hose, must be at least six inches with the latter type of hose bridge described above approaching seven inches; requiring such hose bridges to be traversed by vehicles at very low speeds and generally requiring some arrangement to avoid the hose bridge from being moved by the force of vehicle tires against the sides thereof. Such a height also exceeds the ground clearance of many automobiles currently in service but cannot be reduced without requiring use of smaller diameter hoses (e.g. 2½ inch nominal outside diameter) which reduce water flow rates and cause pressure drops over even relatively short lengths of hose at high flow rates. For example, at flow rates near one thousand gallons per minute, a pressure drop of 100 psi over fifty feet of 2½ inch diameter hose is not unusual whereas a three hundred foot length of five inch hose would produce a pressure drop of only thirty to forty psi at comparable flow rates.